In the operation of manufacturing plants, human operator errors can cause significant problems. Although the operation of individual process units, such as a crude distillation unit, is usually controlled by an automated control system, such as a distributed control system (DCS), which interacts with the process via sensors and actuators, the human operator generally remains ultimate responsibility for meeting production targets, and complying with safety, environmental and other various constraints. The operator interacts with the automated control system by manually adjusting set points (target values) of controlled variables (CVs), and adjusting control high/low limits of manipulated variables (MVs) and/or CVs.
FIG. 1 illustrates a conventional individual support system 100. In FIG. 1, plant 101 is a monitor and control object run by a computer program. A plant data collecting unit 102 collects monitoring data from the plant 101. A data processing unit 103 processes the collected monitoring data. A running operation guide processing unit 104 provides running operation guide data on the basis of the data processed by the data processing unit 103. A human-machine interface processing unit 105 displays the guide data provided by the running operation guide processing unit 104 on CRTs 107 and 108, and provides necessary data for the responsible individual, such as an operator, production supervisor, technician or process engineer by retrieving it from a database 106 corresponding to an input from the CRT for dialog with the individual.
The operation guide processing unit 104 is optional. It determines the state of the plant 101 on the basis of the plant monitoring data input through the data processing unit 103, and displays the contents to be performed by the operator in predetermined procedures on the CRTs 107 and 108 through the human-machine interface processing unit 105 as guidance to the operator. In response to that guidance display, the operator selects the contents to be executed from a touch panel provided on the CRTs 107 and 108. The selected contents are output to the plant 101 through the human-machine interface processing unit 105 and through the automated control system 109, such as a distributed control system (DCS). In configurations without the operation guide processing unit 104, the data processing unit 103 passes all process-related information directly to the human-machine interface processing unit 105. Particularly, current values of key process variables (CVs, MVs, DVs) are displayed together with settings (set points, limits) that are being applied to the process by the automated control system 109.
The operation contents to be performed by the operator are displayed merely as guidance and are thus provided to the operator in order to assist the operator in making a decision. However, since the system lacks a function for guarding the plant from operations which the operator may select erroneously, there is a risk that the operations which the operator has selected, such as by careless mistake, will be transmitted to the plant 101, thereby causing a serious accident in the plant.
Such erroneous operations may be suppressed when all functions of the automated control system are switched on. But the operator can always switch off some of the automation functions, and manually control the plant units or pieces of equipment by adjusting related set points and limits. In general, such flexibility can be seen as an advantageous in certain situations, such as when the process needs to be quickly transitioned from one operation mode to another. The responsive individual (e.g. operator) can apply his/her experience and cognitive skills that the control system generally cannot. However, decisions that are implemented manually may lead to errors, and the risk that an erroneous operation will be made on operations cannot be eliminated completely. Therefore, there is a need to help prevent erroneous or unusual human operator entries.